The present invention relates to a throttle apparatus for an internal combustion engine and, more particularly, to an electronic control throttle device which controls opening and closing a throttle valve by driving an electric driven actuator based on a control signal.
In the electronic control throttle apparatus for controlling a throttle valve of an engine by driving an electric driven actuator (for example, a direct current motor, a stepping motor), a technology known is that an initial opening degree (default opening degree) of the throttle valve in an off state of engine key (in other words, at not energized state of the electric driven actuator) is set to a position larger than its full close position.
Here, the full close position does not mean a position for completely choking the intake air passage. Particularly, in a throttle device performing idling rotating speed control using only a throttle valve without any bypass passage for bypassing the throttle valve, the full close position is defined by classifying into a mechanical full close position and an electrical full close position to be described below.
The mechanical full close position means a minimum opening degree position of a throttle valve determined by a stopper, and the minimum opening degree is set at a position to slightly open the throttle valve from a position to completely choking the intake air passage in order to prevent the throttle valve from sticking. The electrical full close position means a minimum opening degree within a range of opening degrees used for control, and the minimum opening degree is set at an opening position slightly larger than the mechanical full close position in taking the mechanical full close position as the reference by controlling of driving the electric driven actuator (for instance, a position larger than the mechanical full close position by approximately 1xc2x0). In the electronic control throttle device, the electrical full close position (the minimum opening degree on the control purpose) does not always agree with an idling opening degree (an opening degree necessary for idling rotating speed control). The reason is that because the opening degree of the throttle valve is feedback controlled based on an idling rotating speed detected signal in order to keep the idling rotating speed to a target rotating speed, and thereby the opening degree can not be determined uniquely.
In regard to a full open position, there are a mechanical full open position determined by a stopper and an electrical full open position of a maximum opening degree on control. Therein, in a case of simply describing a xe2x80x9cfull close positionxe2x80x9d, meaning of the word includes the electrical full close position as well as the mechanical full close position. In a normal control, the throttle valve is controlled between the electrical full close position (the minimum opening degree in the control range) and the electrical full open position (the maximum opening degree in the control range). By doing so, a part of the throttle valve does not hit on the stoppers for determining the mechanical full close position and the mechanical full open position at controlling the throttle valve to the minimum and the maximum opening degrees. Therefore, mechanical fatigue, abrasion and damage of the stoppers and the gear members can be prevented and sticking of the throttle valve to the stopper can be prevented.
A default opening degree (that is, the initial opening degree in an off state of engine key) is set to an opening degree of a position in which the throttle valve is further opened wider than that in the full close position (the mechanical full close position and the electrical full close position)(for example, a position larger than the mechanical full close position by 4 to 13xc2x0). One reason why the default opening degree is set is that an air flow rate necessary for combustion of pre-warming-up operation at stating-up of the engine (cold starting-up) is secured without any auxiliary air passage (an air passage bypassing the throttle valve). During idling operation, as the engine is warmed up, the throttle valve is controlled so as to moved from the default opening degree toward the smaller opening degree. However, the lower limit is the electrical full close position. Another reason why the default opening degree is set is to cope with requirements for securing self-running (limp home) or for securing an intake air flow rate to prevent the engine operation from stopping even if the throttle control system is failed, for preventing the throttle valve from fixing to an inner surface of the throttle body with a viscous substance or ice.
As conventional examples of default opening degree setting mechanisms, various kinds of default opening degree setting mechanisms are proposed in, for example, Japanese Patent Application Laid-Open No.63-150449, U.S. Pat. No. 4,947,815 and the corresponding patent of Japanese Patent Application Laid-Open No.2-500677, Japanese Patent Application Laid-Open No.62-82238 and the corresponding patent of U.S. Pat. No. 4,735,179 by the same applicant of the present invention, Japanese Patent Application Laid-Open No.10-89096, Japanese Patent Application Laid-Open No.10-131771 and so on.
There are various types of default opening degree setting mechanisms. For example, one type is that a default opening degree is secured by setting the relationship between forces of a returning spring for acting a force toward a closing direction of the throttle valve and an opposed spring (called as a default spring or an initial opening degree spring) for acting a force toward an opening direction of the throttle valve opposing against the force of the returning spring so that the force of the default spring is larger than the force of the returning spring at the default opening degree position and so that a free end of the default spring is stopped by a default stopper at the default opening degree position when the engine key is switched off (for example, Japanese Patent Application Laid-Open No.2-500677).
Another type is, as disclosed in Japanese Patent Application Laid-Open No.1-131771, that a fixing side engaging element to be fixed to a throttle valve shaft (this engaging element may be constructed by a throttle lever, or a gear for transmitting motor power may be used instead of the engaging element) and a moving side engaging element (a linking lever) idly inserted onto the throttle valve shaft and rotatable relative to the throttle valve shaft are provided, and the moving side engaging element and the fixing side engaging element are linked together with a returning spring so as to attract each other, and a force is applied using a default spring onto the moving side engaging element in a direction of opening the throttle valve to engage and rotate the moving side engaging element and the fixing side engaging element (the throttle valve shaft) together opposing against the force of the default spring when the opening degree is within the range smaller than the default opening degree (smaller than the default stopper position), and to rotate only the fixing side engaging element and accordingly the throttle valve shaft opposing against the force of the returning spring and preventing movement of the moving side engaging element by the default stopper when the opening degree is within the range larger than the default opening degree. On the contrary, there is a type that the moving side engaging element and the fixing side engaging element are linked together with the default spring so as to attract each other, and a force is applied using the returning spring onto the moving side engaging element in a direction of closing the throttle valve to engage and rotate the moving side engaging element and the fixing side engaging element (the throttle valve shaft) together opposing against the force of the returning spring when the opening degree is within the range larger than the default opening degree, and to rotate only the fixing side engaging element (the throttle valve shaft) opposing against the force of the default spring and preventing movement of the moving side engaging element by the default stopper when the opening degree is within the range smaller than the default opening degree.
The electronic control throttle device can more accurately perform air flow rate control suitable for operation of an internal combustion engine than a mechanical throttle device in which an amount of stepping-in of the accelerator pedal is transmitted to a throttle valve shaft through an accelerator wire. However, since the electronic control throttle device has the electric drive actuator and the default opening degree setting mechanism, number of the parts is increased and accordingly it is important how to make the throttle body small in size, light in weight and simple in structure and how to simplify the wiring (wire harness).
Further, the electronic control throttle device controls the idling rotating speed by controlling opening degree of the throttle valve, but has the following point to be improved.
In a case where idling rotating speed control is performed with the throttle valve in the electronic control throttle device, an opening degree larger than the mechanical full close position by a certain angle (for example, 5 to 10xc2x0) is secured at least as the minimum opening degree in the control range. Since a gap (sometime called as a shaft support gap) between the throttle valve shaft and a shaft inserting through hole provided in a wall of the throttle body which guides the throttle valve shaft to a bearing practically serves as a part of the intake air passage and the air flow rate (leak air flow rate) flowing through the shaft support gap cannot be controlled, the minimum opening degree in the control range is set with taking it into consideration that the leak flow rate flows into the internal combustion engine.
However, according to the conventional set value of the minimum opening degree for the control range (the electrical full close position), when the throttle valve is closed from the maximum opening degree for the control range (the electrical full open position) toward the minimum opening degree (the electrical full close position, in the idling state), a magnitude of overshoot becomes larger than the minimum opening degree in the closing direction (the overshoot is approximately 1.5xc2x0 at maximum) because the driving force of the motor (the electric drive actuator) is decreased at high temperature or at low temperature (that is, the torque of the motor is reduced at high temperature due to increase in the resistance of the motor, and the torque of the motor is reduced at low temperature due to decease in the battery voltage). As a result, as shown by a solid line {circle around (1)} in FIG. 17, the throttle valve hits on the stopper at the mechanical full close position (the diagonally shaded area in FIG. 17 indicates a state that movement of the throttle valve is blocked by the full close stopper.), and over-current flows in the motor likely to cause an erroneous fail-safe diagnosis (an erroneous diagnosis judging of occurrence of failure in the motor from the over current) or decrease in the lifetime of the motor.
An object of the present invention is to make an electronic control throttle device having an electric drive actuator, a gear mechanism, a default opening degree setting mechanism small in size, light in weight and simple in assembling and wire harness by solving the above-mentioned problems.
Another object of the present invention is to improve reliability of the electronic control throttle device by preventing the throttle valve from hitting on the stopper even if such an overshoot as described above occurs in the throttle valve.
The present invention is basically constructed as follows.
A throttle device for an internal combustion engine according to one aspect of the present invention includes an electric drive actuator and a default opening degree setting mechanism, wherein
a gear case for containing a gear mechanism to transmit power of the electric drive actuator to a throttle valve shaft is arranged on an outer wall of a throttle body, and
a returning spring for acting a spring force on the throttle valve in a closing direction and a spring (a default spring) for acting a spring force on the throttle valve in a direction toward a side of the default opening degree seeing from the full close position of the throttle valve have diameters different from each other, and both of the springs are held around a shaft of said throttle valve shaft and arranged between a gear attached to the throttle valve shaft in the gear mechanism and a wall portion of the throttle body.
According to the above-mentioned construction, the returning spring and the default spring can be intensively arranged between the gear provided in the throttle shaft and the wall portion of the throttle body, and accordingly the part space can be rationalized. Particularly, according to the present invention, by arranging the returning spring and the default spring in such a feature that at least a part of the returning spring and a part of the default spring are overlapped with each other (one spring having a smaller diameter is inserted inside the other spring having a larger diameter), an arranging space in a longitudinal direction of the springs can be shortened, and accordingly this structure is useful in that the gear case and the whole throttle body can be made small in size, light in weight and simple in assembling.
In addition to the above-mentioned construction, the present invention proposes a construction that the spring arranged outside out of the returning spring and the default spring (the spring having the larger diameter) is placed in being guided by an outer periphery of a bearing containing boss for the throttle valve shaft projecting inward of the gear case in a manner that one end of the spring having the larger diameter is fixed to the wall portion of the throttle body. By doing so, the outer periphery of the bearing containing boss for the throttle valve shaft can be used for a space placing one spring out of the returning spring and the default spring. Accordingly, this structure is useful in that the parts can be more intensively arranged, and the throttle body can be made smaller in size and light in weight. Although the other various dependent invention in regard to the first invention are proposed, these will be described in the item of DESCRIPTION OF THE PREFERRED EMBODIMENTS later.
In an electronic control throttle device according to another aspect of the present invention, a throttle body, a motor case containing a motor composing an electric drive actuator and a containing portion of a connector connecting by plugging to a motor terminal provided in an end plate of said motor are formed in a unit. In addition, a motor terminal extracting port for exposing the motor terminal to the containing portion of the connector is formed on a bottom portion of the motor case, and a guide for guiding the connector to the motor terminal extracting port when the connector is plugged to the motor terminal is formed on an inner wall surface of the containing portion of the connector.
By constructing as described above, the connector can be easily connected to the motor terminal without difficulty of positioning the connector to the motor terminal because by containing the motor in the motor case the motor terminal can be seen in the containing portion of the connector (the terminal connector) through the terminal extracting port, and in this state the terminal connector is inserted from the terminal containing portion using the guide. Even if the motor terminal is, particularly, placed in a deep position of the connector containing portion and behind the other parts, the connector can be inserted by being guided by the above-mentioned guide without difficulty while being positioned.
In an electronic control throttle device according to a further aspect of the present invention, a motor case for containing a motor composing the electric drive actuator is integrated with a throttle body in a unit. In addition, in the throttle body, a motor terminal extracting port is formed in a side of a bottom portion of the motor case, a containing space of a connector to be connected to the motor terminal being formed adjacent to the side of the bottom portion of said motor case, the containing space of the connector and a containing space for containing a throttle sensor provided at one end of a throttle valve shaft being formed in one room, a wire lead portion of the throttle sensor being arranged in being directed to the containing space of the motor terminal connector.
By constructing as described above, the wires led from the terminal of the throttle sensor and the wires led from the motor terminal can be merged at adjacent positions in the beginning in the connector and throttle sensor containing space (one room), and accordingly these wires can be gathered without difficulty and can be extracted out of the throttle body. Therefore, this construction is useful to simplify the wiring work and the part assembling work.
An electronic control throttle device according to a further aspect of the present invention, a motor case for containing a motor composing the electric drive actuator and a gear case for containing a gear mechanism to transmit power of the motor to a throttle valve shaft are integrated in a unit. In addition, a motor inserting port of the motor case is opened to the gear case, the motor being attached to the motor case by fastening a motor bracket to triangular point arranged screw holes provided a periphery of the motor inserting port with three screws in total, three sides forming a contour of the motor bracket being curved lines, a motor positioning portion fitting to the three curved lines of the motor bracket to position the motor being formed in the gear case.
By constructing as described above, vibration of the motor can be suppressed more effectively than in a conventional one in which the motor bracket is fastened at two points with screws, and further accuracy of positioning the motor can be improved.
An electronic control throttle device according to a further aspect of the present invention includes an electric drive actuator for opening and closing a throttle valve based on a signal controlling an intake air flow rate of the internal combustion engine. In addition, a gap (a shaft supporting gap) between a throttle valve shaft and a shaft inserting through hole for guiding the throttle valve shaft to a bearing provided in a wall portion of a throttle body is filled with an air leak preventing material, and a minimum opening degree on control purpose of the throttle valve is set to a value larger than an amount of overshoot of the throttle valve occurring when opening degree of the throttle valve is changed from a maximum opening degree on control purpose of the throttle valve to the minimum opening degree.
By constructing as described above, since the intake air flow rate (the leak air flow rate) supplied to the internal combustion engine through the so-called shaft supporting gap of the throttle valve shaft can be eliminated, the minimum opening degree on the control purpose of the throttle valve can be increased larger than in the conventional one by that amount. In the present invention, by making use of this fact the minimum opening degree in the control range is set a value larger than the overshoot of the throttle valve when opening degree of the throttle valve is changed from the maximum opening degree on control purpose of the throttle valve to the minimum opening degree. For instance, by applying the air leak preventing material (for example, molybdenum disulfide), as shown by the solid line {circle around (2)} in FIG. 17, since the minimum opening degree on the control range can be set a value larger than the mechanical full close position by approximately 2xc2x0, the minimum opening degree on the control range can be increased higher by a value corresponding to the overshoot (for instance, approximately 1.5xc2x0) when opening degree of the throttle valve is changed from the maximum opening degree on control purpose (the electrical full open position) to the minimum opening degree (the electrical full close position). Therefore, the stopper blocking element in the side of the throttle valve can be prevented from hitting on the stopper (the full close stopper) determining the mechanical full close position even if the overshoot occurs. Accordingly, even if the overshoot occurs, it is possible to prevent over current from flowing in the motor.
The above-mentioned operation and effect are attained on the premises that the gap (the shaft supporting gap) between the throttle valve shaft and the shaft inserting through hole for guiding the throttle valve shaft to the bearing provided in the wall portion of the throttle body is filled with the air leak preventing material. The above-mentioned operation and effect can not be expected in a mechanical throttle device in which a stepping amount of an accelerator is transmitted to a throttle valve shaft through an accelerator wire even if the so-called shaft supporting gap is filled with the air leak preventing material. The reason is as follows. The idling opening degree in the mechanical throttle device is set to a position where a mechanical full closing stopper exists, and the mechanical throttle device is designed on the premises that the stopper blocking element controlling the throttle valve hits on the full close stopper during operation. Further, since the throttle valve is mechanically driven using the accelerator wire, there is no occurrence of overshoot nor occurrence of over current attendant on the overshoot differently from in the electronic control throttle device.
The Japanese Patent Application Laid-Open No.62-17100 proposes a technology that in a mechanical throttle device, a dryable liquid lubricant (for example, molybdenum disulfide) is penetrated into an air passage formed between a throttle valve shaft and a shaft inserting through hole in a wall portion of the throttle valve assembly (the shaft supporting gap) and dried to fill the air passage with the lubricant solidified and fixed to the air passage. On the background that an idling rotating speed of an engine is set in taking the amount of the air flowing through the so-called shaft supporting gap into consideration since the air flowing through the gap can not be controlled by the throttle valve, but the idling rotating speed is gradually decreased and finally the engine may be stopped because combustion products (combustion soot, viscous substance or the like) are gradually accumulated in the shaft supporting gap. Therefore, the setting of the idling rotating speed is performed by eliminating the gap in the beginning to eliminate the change in the idling air flow rate with time and by using a full close stopper (an idling adjust screw).
In the electronic control throttle type, the idling rotating speed control can be performed by controlling the throttle valve opening degree through feedback control (that is, the idling opening degree is not determined using the idling adjusting screw used in the mechanical throttle device). Therefore, even if combustion products are gradually accumulated in the shaft supporting gap of the throttle valve shaft, decrease in the air flow rate (decrease in the idling rotating speed) caused by the accumulation of the combustion products can be compensated by controlling the throttle valve opening degree. From this point of view, the above-mentioned problem specific to the mechanical throttle device (the problem of the decrease in idling rotating speed caused by accumulation of combustion products in the shaft supporting gap) does not occur in the electronic control throttle device. In other words, there are differences in problem to be solved and in object between the air leak preventing material applied to the shaft supporting gap in the electronic control throttle device and the air leak preventing material applied to the shaft supporting gap in the mechanical throttle device.
In an electronic control throttle device according to a further aspect of the invention, an electromagnetic shield member of a wire used for driving control of the electric drive actuator is a woven shield composed of a tube-shaped member formed by weaving glass fiber and a woven thin metal wire member covering the tube-shaped member.
A conventional electromagnetic shield member of this kind is formed by covering a tube made of silicon rubber with a shielding outer cover of woven thin metal wires. The electromagnetic shield member of the above-mentioned structure can substantially reduce its cost and can effectively shield electromagnetic wave compared to the conventional electromagnetic shield member.